Method for melt-spinning polyester microfilaments having a maximum dtex of 0.7 and polyester microfilaments that can be produced according to this method

ABSTRACT

The invention relates to a method for melt-spinning polyester microfilaments having a maximum dtex of 0.7 and to microfilaments that can be produced according to this method. According to the invention, the filaments, according to their titer, are spun from a melt with a solution viscosity lower than that of the prior art.

The present invention concerns a method for the melt spinning ofpolyester microfilaments with a titre of not more than 0.7 dtex and thepolyester microfilaments manufactured thereby.

According to the state of the art, in filament melt spinning a polymermelt is delivered to the spinneret plates from an extruder or from apolycondensation plant by spinning pumps. After emerging of the meltfrom the capillary bores of the spinneret plates in the form of finefilaments, these filaments are cooled by means of a cooling system, forexample, by blowing with air, then combined, bundled, subjected tospinning preparation and, if occasion arises, wound at very high speeds,for example, at more than 2000 m/min.

For more than 10 years in polymer spinning technology a development hasbeen emerging for the manufacture of filament yarns with finer and finersingle-filament titres, so-called microfilaments with titres of lessthan 1 dtex.

The usual microfilament yarns for further processing of textiles are,according to the present-day state of the art, preferably composed ofmore than 100 single filaments.

Products of so many microfilaments are distinguished by specialproperties which are advantageous to the consumer.

For anyone skilled in the art, the melt spinning of microfilaments isnot by any means trivial. Exit of the polymer melt from the fine nozzlebores and cooling of the filaments are very important steps in theprocess, because their uniformity very substantially affects the massuniformity, the textile properties such as strength and elongation andparticularly the uniformity and quality of dyeing of the microfilamentsand of the yarns assembled therefrom.

Thus, constant temperature control in the high-viscosity polymer meltwith little material flow up to the spinneret plate and through thecapillary bores poses considerable problems for extremely fine filamenttitres. At excessively high spinning temperatures the polymers degradeall the faster, lower temperatures lead to greater irregularities amongthe filaments of the same spinneret plate and increased breaks ofindividual filaments or of the whole filament bundle upon exit from thespinneret plate.

According to the state of the art, polymers having melt viscositieswhich lie outside the range of so-called spinning grades cannot be spun.

For polyethylene terephthalate these are, for example, between 130 and150 Pa·s 290° C., which corresponds to relative solution viscosities(1.0% in m-cresol at 20° C.) from eta rel. 1.60 to 1.65.

For the present invention, the object was therefore to provide a methodfor the melt spinning of polyester microfilaments with titres of lessthan 1.0 dtex, which with spinning performance allows the manufacture offilaments and the filament yarns assembled therefrom with very uniformtextile properties and above all with particularly uniform dyeing.

This object is achieved by the method for the melt spinning of polyestermicrofilaments with a titre of not more than 0.7 dtex.

Surprisingly, in spinning tests it turned out that polyestermicrofilaments can, unlike the state of the art known hitherto,perfectly well be spun at lower viscosities than correspond to theso-called spinning grades for filament spinning.

It even proved particularly advantageous for the spinning performance ofsuch microfilaments with titres of less than 0.7 dtex if the polymermelt has a reduced relative solution or melt viscosity compared with theusual spinning grades.

Thus in particular for polyethylene terephthalate a clear correlationcan be formulated between filament titres of between 0.1 and 0.7 dtexand the viscosity, whereby the spinning performance is excellent and thedye ability of the microfilaments and of the filament yarns assembledtherefrom is outstanding.

According to the formula:(0.1052×InX)+1.649=eta rel.polyethylene terephthalate microfilaments within the range between 0.1and 0.7 dtex can be spun without problems, the spinning speed being 2500m/min±10% and the resulting breaking elongation (BE) of the POYfilaments being between 95 and 120%. Here, X stands for the filamenttitre (DTY titre) in dtex, and the relative solution viscosity eta rel.is measured 1% in m-cresol at 20° C.

Defined filament titres can easily be spun at the calculated viscositieswith a breadth of fluctuation of relative solution viscosity of about±0.05 still with the same good results at a defined spinning speed of2500 m/min, for example.

Within this relationship it is possible, for example, to spinmicrofilaments with a titre of 0.34 dtex from polyethylene terephthalatewith a relative solution viscosity eta rel. around 1.53, those of 0.23dtex with eta rel. around 1.49 and of 0.1 dtex with eta rel. around1.41.

The reduced polyethylene terephthalate viscosities thus used for themelt spinning of microfilaments are therefore advantageously within aneta rel. range of approx. 1.40 to 1.59.

By the process according to the invention, microfilaments with a titreof not more than 0.7 dtex can be spun, preferably those with titres ofbetween 0.1 and 0.35 dtex and particularly preferably between 0.1 and0.2 dtex, wherein as a particular advantage the total spin breaks whichare known for microfilament spinning due to the tearing of all thefilaments at the spinneret plate are absent within all titre ranges.

The relative solution or melt viscosities can be directly predeterminedby polycondensation or the spinning granulate. They can be adjustedequally advantageously by adding additives which selectively lower theviscosity, to the polymer melt or to the spinning granulate in theextruder.

Basically, spinning speed of between 2000 and 3300 m/min can also beused for the aforementioned titre range, wherein adapted viscosities canbe used for optimising of the spinning performance and uniformity ofdyeing.

In an advantageous manner, diols are suitable as additives, and in aparticular manner even alcohols or water.

Among the diols, ethylene glycol, diethylene glycol and particularlytriethylene glycol are preferred.

For instance, triethylene glycol is added to the polyethyleneterephthalate melt in quantities from 0.1 to 0.4 wt. % in order toobtain relative solution viscosities within the range from 1.4 to 1.59.

The invention also includes polyester microfilaments with a titre of notmore than 0.7 dtex which can be manufactured by the method according tothe invention and which are distinguished by a grey scale value foruniformity of dyeing from 4.5 to 5.0. This uniformity of dyeing is ofparticular value for textile further processing of the microfilamentsaccording to the invention and of the filament yarns assembledtherefrom, as it is well known to anyone skilled in the art that even incase of high uniformity of the textile properties according to thecommon Uster values U and U1/2 marketable yarns can still exhibit lackof uniformity of dyeing which is obtrusive in further processing.

To determine the uniformity of dyeing of the microfilaments,microfilament yarns in a knitted hose were dyed with a test dye andmeasured in a spectral photometer, and the L,a,b values determined.

In the process, samples which were taken from different spinninglocations of a semi-industrial plant over 24 hours yielded results withexcellent delta E values which without exception were below 1.0 andpreferably below 0.9.

By the method according to the invention, the microfilaments can also bespun-dyed in a preferred manner.

The microfilaments according to the invention are suitable for furtherdrawing and for thermal and/or mechanical treatment, for example, forspinning/drawing/texturing. They can also be further processed intohighly oriented filament yarns.

Examples 1a to 1d illustrate the invention:

EXAMPLES

“Method for the Melt Spinning of Polyester Microfilaments with a Titreof not more than 0.7 dtex and Polyester Microfilaments ManufacturedThereby” Total titre dtex 88.0 88.0 56.0 56.0 Single filament dtex 0.460.46 0.29 0.29 titre Spinning speed m/min 2500 2500 2500 2500 Meltingpoint ° C. 295 295 295 295 Chips viscosity m- 1.640 1.640 1.640 1.640cresol Reduced vis- m- 1.510 1.560 1.470 1.630 cosity cresol TEGaddition % 0.20 0.10 0.31 — Spin perfor- very good good very good notmance spinnable

POY Data: Uster ½ U % 0.27 0.36 1.1 — Uster U % 0.45 0.67 2.4 — TenacitycN/dtex 2.6 2.8 2.3 — Elongation % 105 98.0 117 —

DTY Data: Spinning/drawing/texturing very good good good — Singlefilament titre dtex 0.34 0.34 0.23 — Total titre dtex 65.4 65.8 43.2 —Tenacity cN/dtex 3.3 3.3 2.7 — Elongation % 23.3 23.1 24.5 — Boilingwater shrinkage % 4.2 4.1 2.1 —

Colour Assessment: Grey scale 5 4 6 — HunterLabb −33.8 −32.4 −30.6 —SDEV(b) 0.12 0.19 0.35 — delta E max 0.4 0.5 1.0 —

1. Process for the melt spinning of PES microfilaments with a titre ofnot more than 0.7 dtex, characterised in that the microfilaments arespun as partially oriented yarn (POY) at spinning speeds from 2250 to3300 m/min from the melt of a polyester with reduced relative solutionviscosity compared with PES fibre spinning grades with relative solutionviscosities of between 1.60 and 1.65 as a function of their titre,wherein the relative solution viscosity reduced as a function of titreis determined according to the formulaeta rel=(0.1052×InX)+1.649, where X is the filament titre in dtex, andwherein the spin performance of defined filament titres can be realisedwith a breadth of fluctuation of relative solution viscosity of ±0.05.2. Process according to claim 1, characterised in that the polyestermelt is polyethylene terephthalate.
 3. (canceled)
 4. Process accordingto claim 2, characterised in that the reduced relative solutionviscosity of the polyethylene terephthalate melt is adjusted by addingand homogeneously mixing in at least one viscosity-regulating additive.5. Process according to claim 4, characterised in that the additive isselected from the group comprising aliphatic diols and water.
 6. Processaccording to claim 5, characterised in that the aliphatic diol isselected from the group comprising triethylene glycol, diethylene glycoland ethylene glycol.
 7. Process according to claim 1, characterised inthat filaments with titres from 0.1 to 0.7 dtex are spun.
 8. Processaccording to claim 7, characterised in that filaments with titres from0.1 to 0.35 dtex are spun.
 9. Process according to claim 7,characterised in that filaments with titres from 0.1 to 0.2 dtex arespun.
 10. Polyester microfilaments with a titre of not more than 0.7dtex, manufactured according to claim 1, characterised in that they havea dyeing uniformity value according to grey scale from 4.0 to 5.0 and adelta E value of less than 1.0.